(1) Field of the Invention
The present invention relates to a computer network system where a plurality of user stations or data terminals are attached over a data transmission network to one or a plurality of host processors.
(2) Prior Art
An overview of the architecture used in computer networks is given in an article by S. Wecker, "Computer Network Architectures," Computer, September 1979. Another similar overview including a description of the SNA (Systems Network Architecture) network is provided in an article by P. E. Green, "An Introduction to Network Architectures and Protocols," in the IBM Systems Journal, Vol. 18, No. 2, 1979. In these articles the various available computer networks such as SNA, DNA, ARPANET, etc. are described by means of hierarchical architectural layers, where the lowest layer relates to the physical communication lines interconnecting the various user nodes of the network and where the highest level concerns the conversation per se between the various end users of the network.
Computer network systems have been subject to standardization work by the International Organization for Standardization (ISO) and in a paper by Herbert Zimmerman, "OSI Reference Model--The ISO Model of Architecture for Open Systems Interconnection," IEEE Transactions of Communications, April 1980, the architecture described includes seven layers: physical, data link, network, transport, session, presentation and application layer. The present invention concerns primarily the session layer, which relates to the establishment, termination and control of a session between two end users of a network.
In an IBM SNA (Systems Network Architecture) network, a plurality of information units are circulating in the network between pairs of end users when sessions have been established between such pairs. These information units are of various types and hierarchical levels according to the various layers they are representing. A description of such information units and their use in established sessions is provided in an article by James D. Atchins, "Path Control: The Transport Network of SNA," IEEE Transactions on Communications, April 1980.
The extensive growth and use of data networks in today's society has opened up a number of new possibilities in modern data communication technology.
On data networks there are many more parties, capable of communicating with one another than on networks built with leased lines.
There are also many applications, requiring communication between two parties only during a short interval of time, for example, seat reservation and banking applications.
In this environment a large amount of computer resources would be required to perform the computer session establishment function for the individual pairs to communicate with one another. The Nordic Public Data Network, as described in the publication, "The Public Data Networks in the Nordic Countries," published in March 1978 by the Swedish PTT, is an example of a computer network using switched lines (circuit switching).